<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Function template skip</title>
<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset">
<link rel="up" href="../xpressive/reference.html#doxygen.regex__primitives_8hpp" title="Header &lt;boost/xpressive/regex_primitives.hpp&gt;">
<link rel="prev" href="namespaceboost_1_1xpressive_1ad58db5547a515b013bd1869db1ccaabf.html" title="Function template imbue">
<link rel="next" href="structboost_1_1xpressive_1_1regex__traits__version__1__tag.html" title="Struct regex_traits_version_1_tag">
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td>
<td align="center"><a href="../../../index.html">Home</a></td>
<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td>
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
<td align="center"><a href="../../../more/index.htm">More</a></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="namespaceboost_1_1xpressive_1ad58db5547a515b013bd1869db1ccaabf.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../xpressive/reference.html#doxygen.regex__primitives_8hpp"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="structboost_1_1xpressive_1_1regex__traits__version__1__tag.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
</div>
<div class="refentry">
<a name="doxygen.namespaceboost_1_1xpressive_1a35b352ec2526d1d2427751ac4f834126"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Function template skip</span></h2>
<p>boost::xpressive::skip — Specify which characters to skip when matching a regex. </p>
</div>
<h2 class="refsynopsisdiv-title">Synopsis</h2>
<div class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../xpressive/reference.html#doxygen.regex__primitives_8hpp" title="Header &lt;boost/xpressive/regex_primitives.hpp&gt;">boost/xpressive/regex_primitives.hpp</a>&gt;

</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Skip<span class="special">&gt;</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="identifier">skip</span><span class="special">(</span><span class="identifier">Skip</span> <span class="keyword">const</span> <span class="special">&amp;</span> skip<span class="special">)</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="id-1.3.44.5.10.63.4"></a><h2>Description</h2>
<p><code class="computeroutput"><a class="link" href="namespaceboost_1_1xpressive_1a35b352ec2526d1d2427751ac4f834126.html" title="Function template skip">skip()</a></code> instructs the regex engine to skip certain characters when matching a regex. It is most useful for writing regexes that ignore whitespace. For instance, the following specifies a regex that skips whitespace and punctuation:</p>
<pre class="programlisting"><span class="comment">// A sentence is one or more words separated by whitespace</span>
<span class="comment">// and punctuation.</span>
<a class="link" href="structboost_1_1xpressive_1_1basic__regex.html" title="Struct template basic_regex"><span class="identifier">sregex</span></a> <span class="identifier">word</span> <span class="special">=</span> <span class="special">+</span><a class="link" href="namespaceboost_1_1xpressive_1a1dc091385c7f62d5288156dd0b2a4baa.html" title="Global alpha"><span class="identifier">alpha</span></a><span class="special">;</span>
<a class="link" href="structboost_1_1xpressive_1_1basic__regex.html" title="Struct template basic_regex"><span class="identifier">sregex</span></a> <span class="identifier">sentence</span> <span class="special">=</span> <a class="link" href="namespaceboost_1_1xpressive_1a35b352ec2526d1d2427751ac4f834126.html" title="Function template skip"><span class="identifier">skip</span></a><span class="special">(</span><a class="link" href="namespaceboost_1_1xpressive_1a41aeb0b5257a91ac34d336aa86b59bae.html" title="Global set"><span class="identifier">set</span></a><span class="special">[</span><a class="link" href="namespaceboost_1_1xpressive_1ab34b82560c0e1148b5c1748351711294.html" title="Global _s"><span class="identifier">_s</span></a> <span class="special">|</span> <a class="link" href="namespaceboost_1_1xpressive_1a557079c0471795432b282ff7acbbc197.html" title="Global punct"><span class="identifier">punct</span></a><span class="special">]</span><span class="special">)</span><span class="special">(</span> <span class="special">+</span><span class="identifier">word</span> <span class="special">)</span><span class="special">;</span>
</pre>
<p>The way it works in the above example is to insert <code class="computeroutput">keep(*set[_s | punct])</code> before each primitive within the regex. A "primitive" includes terminals like strings, character sets and nested regexes. A final <code class="computeroutput">*set[_s | punct]</code> is added to the end of the regex. The regex <code class="computeroutput">sentence</code> specified above is equivalent to the following:</p>
<pre class="programlisting"><a class="link" href="structboost_1_1xpressive_1_1basic__regex.html" title="Struct template basic_regex"><span class="identifier">sregex</span></a> <span class="identifier">sentence</span> <span class="special">=</span> <span class="special">+</span><span class="special">(</span> <a class="link" href="namespaceboost_1_1xpressive_1ad009f0422d798ec20af8c18bec5c8325.html" title="Function template keep"><span class="identifier">keep</span></a><span class="special">(</span><span class="special">*</span><a class="link" href="namespaceboost_1_1xpressive_1a41aeb0b5257a91ac34d336aa86b59bae.html" title="Global set"><span class="identifier">set</span></a><span class="special">[</span><a class="link" href="namespaceboost_1_1xpressive_1ab34b82560c0e1148b5c1748351711294.html" title="Global _s"><span class="identifier">_s</span></a> <span class="special">|</span> <a class="link" href="namespaceboost_1_1xpressive_1a557079c0471795432b282ff7acbbc197.html" title="Global punct"><span class="identifier">punct</span></a><span class="special">]</span><span class="special">)</span> <span class="special">&gt;&gt;</span> <span class="identifier">word</span> <span class="special">)</span>
                       <span class="special">&gt;&gt;</span> <span class="special">*</span><a class="link" href="namespaceboost_1_1xpressive_1a41aeb0b5257a91ac34d336aa86b59bae.html" title="Global set"><span class="identifier">set</span></a><span class="special">[</span><a class="link" href="namespaceboost_1_1xpressive_1ab34b82560c0e1148b5c1748351711294.html" title="Global _s"><span class="identifier">_s</span></a> <span class="special">|</span> <a class="link" href="namespaceboost_1_1xpressive_1a557079c0471795432b282ff7acbbc197.html" title="Global punct"><span class="identifier">punct</span></a><span class="special">]</span><span class="special">;</span>
</pre>
<div class="important"><table border="0" summary="Important">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../doc/src/images/important.png"></td>
<th align="left">Important</th>
</tr>
<tr><td align="left" valign="top"><p>Skipping does not affect how nested regexes are handled because they are treated atomically. String literals are also treated atomically; that is, no skipping is done within a string literal. So <code class="computeroutput">skip(_s)("this that")</code> is not the same as <code class="computeroutput">skip(_s)("this" &gt;&gt; as_xpr("that"))</code>. The first will only match when there is only one space between "this" and "that". The second will skip any and all whitespace between "this" and "that".</p></td></tr>
</table></div>
<p>

</p>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Parameters:</span></p></td>
<td><div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term"><code class="computeroutput">skip</code></span></p></td>
<td><p>A regex that specifies which characters to skip. </p></td>
</tr></tbody>
</table></div></td>
</tr></tbody>
</table></div>
</div>
</div>
<div class="copyright-footer">Copyright © 2007 Eric Niebler<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="namespaceboost_1_1xpressive_1ad58db5547a515b013bd1869db1ccaabf.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../xpressive/reference.html#doxygen.regex__primitives_8hpp"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="structboost_1_1xpressive_1_1regex__traits__version__1__tag.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>
